Making of rivet head bimetallic electrical contacts

ABSTRACT

A rivet head is formed on a bimetallic electrical contact wire by striking one end of the wire with flat surfaced cam means while retarding the advance of the wire by spring-loaded cam means.

United States Patent Inventor Hans wacker 501 Field of Search 219/154,Heidelberg, Germany 149, 150, 15 1; 72/354, 452, 407, 358; 10/1 1, 15,[21] Appi. No. 767,321 24, 26 221 Filed Oct. 14, 1968 [45] Patented May18, 1971 [56] References Cited [73] Assignee Renz Wacker & C0.,Maschinen-u UNITED STATES PATENTS Y Kettenfabrik 4 1 309 523 7/1919Hosford 219/150 [32] Pnonty Oct. 12, 1967 [33] a any 1,462,775 7/1923Tr1ve1lon1 219/150 [31] P 16 27 696,3 Primary Examiner.i. V. TruheAssistant Examiner-Lawrence A. Rouse Attorneys-Francis D. Stephens andHugo Huettig, Jr. [54] MAKING OF RIVET HEAD BIMETALLIC 4 ELECTRICALCONTACTS 7 Clam 8 mm ABSTRACT: A rivet head is formed on a bimetallicelectrical [52] US. Cl 219/154 contact wire by striking one end of thewire with flat surfaced [51] Int. Cl B21j 5/06, cam means whileretarding the advance of the wire by spring- H05b 1/00 loaded cam means.

TRA NSFORMA TOE Pgtgnted May 18;

2 Sheets-Sheet 2 INVENTOR Hans Wacker MAKING OF RIVET HEAD BIMETALLICELECTRICAL CONTACTS This invention relates to a method and apparatus forthe production of resistance welded-shaped parts and especially tobimetallic welded electrical contacts made of wire in which the contacthead is larger than the diameter of the original wire.

It is the object of this invention to make a more economical productionthan heretofore available and to improve the quality of the finishedproduct with regard to the welding, final shape, technical andelectrical characteristics.

Welded-shaped products, such as bimetallic-welded wire contacts ofdifferent metals, are produced either by cold-press welding orelectrical resistance welding, that is, hot welding.

In the cold-press welding of bimetallic contacts, high pressures areused to enlarge the surfaces of the two metal components such as copperand silver which bear against each other. Since only a limited volume ofboth metals is available for the upsetting, more material is needed thanis actually necessary for the formation of a large head. Thus, incoldpress welding, approximately the same volume of copper and silver isneeded. Also, the length of the metal pieces must be such that they donot become bent during the upsetting process. Also, the rule forcold-press welding is that the quality of the cold weld increasesas thethickness of the welding layers decreases. In order to form the head,however, more material is needed as, forexarnple, copper. When thecopper is fed in making a head, an upsetting fold or crease occursduring the-pressing-which can extend to the stem of a bimetalliccontact. Cold-press welding of a bimetallic contact without anupsettingfold is only possible with small heads which are practicallynever used, that is, up to about 0.6 mm. of the rivet head height.

Bimetallic contacts produced by heat welding can be made without anupsetting fold in a limited manner, that is, with a relatively low headthickness of about I mm.

Upsetting folds made during the formation of the contact cause troublein the finishedcontact. The electrical resistance at the fold becomesgreater and that spot heats up. Since the electrical contacts strikeeach other constantly in the center of the contact surface, the layerswhich have the upsetting folds separate from one another in the courseof time. Above all, this disadvantage occurs in high voltage switches.

Contacts have been produced from strip-plated bands or ribbons which aremade by welding a layer of precious metal, such as fine silver and itsalloys, on a layer of base metal, such as iron or monei, or by solderingunder pressure inwhich a flux is used between the two combined metals.Thereafter discs are stamped out of the fine metallic bands. These discsare fed into presses or stamping tools in which they are upset to formthe finished head and/or welded contact.

The strip-plated bands are also made by the cold-press welding of themetal components. This method is principally currently used in theUnited States. Again, discs are stamped out of the bands, which discsare then formed into the rivet contacts.

The strip-plated bands can also be produced on middle and/or highfrequency automats into which a precious metal and a base metal band arefed. and followed by a welding process. After the welding, the bands aresoft. The final The aforesaid method of producing strip-plated bands hasnumerous disadvantages. The forming of the initial stripplated startingmaterial is very expensive. Because the discs have to be stamped out ofthe striplike plated material, there is a relatively high waste since itis expensive to separate the precious metal from the base metal in thewaste or scrap. F urthermore, the volume rate of production in thesemethods is relatively low. Also, the reduction burning welding machinewith electronic control is very costly.

Up to now it was, therefore, possible to produce bimetallic contactsfrom wires of different metals by cold-pressing or heat welding whereinthe precious metal layer for the most part was composed of silver andits alloys and the base metal was copper. These are combinations ofmetals whose electrical conductivity differs very little from oneanother. It has been impossible up to now to produce the so-called headand/or welded contacts of wires of different metals, on the one hand,because the great difference in their electrical conductivity betweenthe base metal, such as iron or monel, and the coating layer, such assilver and its alloys, and, on the other hand, because of the difficultyin shaping the welding contacts.

In the method and apparatus of this invention, it is now possible toproduce bimetallic contacts as well as head and/or welded contacts fromwires of differentmetals in the required size and with the desired andnecessary characteristics in one and the same machine, which has notheretofore been possible. In this invention, the precious metal wire ina resistance welding process using alternating current is supplied witha diameter which is somewhat smaller than that of the base product istherefor subsequently cold-formed on profile cylinders to obtain thedesired mechanical stability. Following this, again, is the stamping outof the discs and the shaping of the same.

Also, another method is used for the production of the head and/orwelded contacts in that the discs are stamped from the base metal. Thesediscs are fed into reduction welding machines which weld an exactlymeasured coating or layer of precious metal onto the disc from a roll ofwire controlled by an electronically programmedmachine. Following thisis the pressing process to obtain the finished head and/or weldedcontact. This method is principally used in the U.S.A. and in Englandand is known under the term paddling".

metal wire, and in a direct current condenser discharge surge weldingprocess with the diameter that is the same as that of the base metalwire, as well as with various lengths of wire components in relation anddepending upon the difference in the conductivity of the wire ends whichare welded together. The wires are fed toward each other until the twoend abutting surfacesmeet and then are butt welded together in a flatseam. A welded piece of any desired length is then cut off andintroduced into a press for shaping the contact head. Thus for the hotwelding of the two wires in this invention, the length of the metalconductors as well as the diameter of the wires is changed in order toequalize the difference in the electrical conductivity values.

In a further feature of this invention, the head is shaped by means of acontinuous movement of the upsetting die in an assembly line pressingprocess with a simultaneous continuous forward feeding of the initialwire from the support. Following 'the preshaping of the head by means ofthis continuous pressing operation, it is possible to finish the head bymeans of one single upsetting hammer stroke.

The apparatus for performing the method of this invention has a die forholding the wire which is to be upset in which is a rod driven by a camhaving several cam surfaces following one another, the wire being drivenagainst a counter springloaded die which is retarded in movement by acam having a continuous surface. In the cam having several surfaces, thefirst three surfaces form a rising straight line and the following twosurfaces intersect in an-obtuse angle Y.

The means by which the objects of the invention are obtained aredescribed more fully with reference to the accompanying drawings inwhich:

FIG. 1 is a crossasectional view through the welding apparatus;

FIG. 2 is a cross-sectional view through the upsetting rivet head tool;

FIG. 3 is a'view similar to FIG. 2 showing a further step in theupsetting operation;

FIG. 4 is a detailed view of a part of FIG. 3 showing the final form ofthe rivet head;

FIG. 5 is an enlarged cross-sectional view through a partially formedbimetallic contact;

FIG. 6 is a view similar to FIG. 5 showing the finished contact-head;

FIG. 1 is a View similar to FIG. but showing a modified are feedingslides'joined on one side to the welding trans-' former by copper bandsand the other side being connected to shearing knives 5. The distancebetween the contacting ends of the wires 1 and 2 from the shearingknives 5 depends upon the difference in the electrical conductivity ofthe wires being welded and varies in this butt welding process. When thenecessary welding pressure, which is dependent on the wire diameter, isobtained, the welding surges are initiated by means of a transistorizedwelding machine control, not shown, and this causes the welding of theabutting ends of the wires 1 and 2. The electrodes 3 and 4 forming theforward feeding slides are moved into cutting position for the length ofwire desired. The adjustable shearing knife blade 6 moves in thedirection of the arrow C and shears off the length of the welded-wire incooperation with the knives 5. The finger 7 mounted in a reciprocatableslide 8' which moves in the direction of the arrow D picks up thesheared off bimetallic wire 12 and carries it to the entrance of die 9.The springloaded initial die press 10 pushes the bimetallic wire intothe opening in the die 9. which, in turn, is carried by a block 11.Bimetallic wire 12 is then pushed by an upsetting shaft 13 driven by aplunger 14 against the die 10. The plunger 14 has at its opposite ehd acylindrical pin 15 which, in turn, is driven by a continuously risingeccentric cam 16. The spring-loaded initial die 10 which is mounted in arecess 17 attached toa roller slide 18 moves slowly back with itsmovement being controlled by the curved cam 19. The cam surfaceof cam 19is such that the movement is limited to about from L5 to 2 mm. Thus,because the continuously rising cam 16 works together with the. slowlyfalling cam 19, the bimetallic wire, as shown in FIGS. 3 and 5, isgradually formed. The upsetting .shaft 13 for forming the contact has arecess in the end of the shaft for forming a contact with a welding bosson it, as indicated in FIG. 4. If the required finished form cannot beobtained by the continuous pressing operation alone, then the cam can beshaped to give a final upsetting stroke to finish the electricalcontact. If desired, a third cam can be employed for this'purpose.

Two different types of electrical contacts are shown in FIGS. 5 to 8 InFIGS. 5 and 6, the'bimetallic contact has a stern, and in FIGS. 7 and 8the bimetallic contact has a welding boss. FIGS. 5 and 7 show thepreformed contacts, and

FIGS. 6 and 8 show the complete finished contacts. The contact in FIGS.5 and 6 has been welded from two pieces of wire to form a bimetallicrivet contact formed with a layer of precious metal 20 on the head ofbase metal 21 which includes a stem 22. These rivet contacts are usedmainly for the removable and exchangeable contacts with springs, forexample, for switches and relays in the electricalfield. The contactshown in FIGS. 7 and 8 is also made from welded wires so that the finalcontact has a precious metal layer 23 on the head 24 of base metal andwhich includes a welding boss 25. These welded contacts are usedprimarily for the permanent and irreplaceable welding of contact springsand contact bands for switches and relays.

lclaim: f

l. A-method of making bimetallic electrical contacts comprising thesteps of feeding the ends of two elongated wires,

' one-of the base. metal, the other of the precious metal of which thecontact is to bemade, into end to end contact, the 'wires beingsupported by welding electrodes, the lengths of each e ual parts,passing electric current through the wires to effect a utt weld,severing a piece including the welded ends of the wires from the longlengths of wire, placing the severed piece in an upsetting press andshaping the piece to form an electric contact head.

2. The method of claim 1 in which the head is formed in the press bycontinuously advancing the severed piece against a surface moving in thesame direction but at a lesser speed.

3. The method of claim 1 in which the wire of the precious metal wire isof less diameter than the base metal wire.

4. The method of claim 1 in which the diameters of the wires are thesame.

5. The method'of claim 4 in which the electric current is the dischargeof a condenser. I

6. The method of claim I in which the electric welding current is directcurrent.

temating current.

1. A method of making bimetallic electrical contacts comprising thesteps of feeding the ends of two elongated wires, one of the base metal,the other of the precious metal of which the contact is to be made, intoend to end contact, the wires being supported by welding electrodes, thelengths of each wire from its electrode to its contact with the otherwire being such, depending on the electrical conductivity of the wiresas to divide the electrical resistance between the electrodes into equalparts, passing electric current through the wires to effect a butt weld,severing a piece including the welded ends of the wires from the longlengths of wire, placing the severed piece in an upsetting press andshaping the piece to form an electric contact head.
 2. The method ofclaim 1 in which the head is formed in the press by continuouslyadvancing the severed piece against a surface moving in the samedirection but at a lesser speed.
 3. The method of claim 1 in which thewire of the precious metal wire is of less diameter than the base metalwire.
 4. The method of claim 1 in which the diameters of the wires arethe same.
 5. The method of claim 4 in which the electric current is thedischarge of a condenser.
 6. The method of claim 1 in which the electricwelding current is direct current.
 7. The method of claim 1 in which thewelding current is alternating current.